Ignition system for a gas turbine engine



June 30, 1964 J. .1. LAWSER 3,133,924

IGNITION SYSTEM FOR A GAS TURBINE ENGINE Filed June 30, 1960 CK/HMBERJOHN J. 419 W651? IN V EN TOR.

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ATTOR/V'f United States Patent 3,138,924 IGNITION SYSTEM FOR A GASTURBINE ENGINE John J. Lawser, Dearbom, Mich, assignor to Ford MotorCompany, Dearborn, Mich, a corporation of Delaware Fiied June 30, 1960,Ser. No. 39,898

. 1 Claim. (Cl. 6039.14)

This invention relates to a starting and ignition system for a gasturbine engine and more particularly to a starting and ignition systemfor a gas turbine engine in which an igniter is energized from a lowvoltage-high current source simultaneously with the energization of anelectrical power means connected to start said gas. turbine engine.

In gas turbine engines a need exists for a simple and inexpensive meansfor supplying low voltage-high current electrical energy to an igniterpositioned in the combustion chamber of a gas turbine engine at the timethe engine is started. This type of source provides suflicient power forthe igniter and assures long igniter life since the igniter operates atlow voltage. The igniter should preferably be energized simultaneouslywith the energization of the electrical power means that are connectedto rotate the compressor or turbine of the engine.

The applicant has provided a novel solution to this problem by providinga starting and ignition circuit in which an igniter, preferably of theglow plug type, is connected across an electrical conductor connectedbetween a source of electrical energy and an electrical power meansconnected to said gas turbine engine. This arrangement provides a lowVoltage-high current source for the igniter since the voltage dropacross this conductor is quite small and since the high current drawn bythe electrical power means during starting is available.

An object of the invention is the provision of a starting and ignitionsystem for a gas turbine engine that is simple, uncomplicated andinexpensive.

Another object of the invention is the provision of a starting andignition system for a gas turbine engine in which an igniter isenergized from a low voltage-high current source simultaneously with theenergization of a starting circuit for said engine.

A further object of the invention is the provision of a starting andignition system for a gas turbine engine that assures long life for aglow plug igniter employed with the engine.

Other objects and attendant advantages of the present invention willbecome more readily apparent as the specification is considered inconnection with the attached drawing in which the single figure thereofshows the invention is schematic form.

Referring now to the drawing, there is shown a gas turbine engine ofconventional design generally designated by the numeral 11. The gasturbine engine includes a compressor and turbine (not shown). Anelectrical power means preferably starting motor 12 of conventionalelectrical design is adapted to be connected to the gas turbine engine,preferably the compressor thereof, through a coupling, designated by thenumeral 13. The gas turbine engine also includes a combustion chamber 14of conventional construction such as those shown in United StatesPatents 2,768,497, issued October 30, 1956, to C. F. Hayes, and2,872,971, issued February 10, 1959, to I. S. Clarke et al. An igniter15 of the glow plug type is positioned within the combustion chamber 14.This glow plug may be of the type disclosed in my copending applicationSerial No. 693,059, filed October 29, 1957, or the types disclosed in mycopending application Serial No. 693,060, also filed October 29, 1957.These applications have matured into Patents No. 3,017,540 and No.3,017,541, respectively, both issued January 16, 1962.

3,138,924 Patented June 30, 1964 The starting motor 12 and the igniter15 are adapted to be energized from a source of electrical energy, forexample, a storage battery or a plurality of storage batteries,designated by the numeral 16, through an ignition switch 17 thatpreferably takes the form of a relay. The battery includes a negativeterminal 21 connected to ground through a lead 22, and a positiveterminal 23 connected to a first terminal 24 of switch or relay 17through a lead 25. The positive terminal 23 of the battery 16 is alsoconnected to one terminal of relay winding 26 through a hand switch 27and a lead 28. The other end of the relay winding 26 is connected toground through a lead 29. The other terminal 31 of the switch or relay17 is connected to a first terminal 32 of starting motor 12 through alow resistance electrical conductor 33. The other terminal 34 of thestarting motor 12 is connected to ground through a lead 35.

The glow plug igniter 15 is connected across or in parallel with theconductor 33. This is preferably accomplished by having one terminal 36thereof connected through lead 37 to one end of the conductor 33, at theterminal 31 of switch 17, and by having the other terminal 38 connectedthrough lead 39 to the other end of the conductor 33, by a connection tothe terminal 32 of starting motor 12.

In the operation of the device the hand switch 27 is closed therebyenergizing the Winding 26 and closing switch or relay 17. This actionenergizes the starter motor 12 from the battery 16 via lead 25, relay orswitch 17, and electrical conductor 33. Although the electricalresistance of the electrical conductor is low, a small voltage drop willoccur between terminals 31 and 32. This causes a current to flow in theglow plug igniter 15 to bring it to its incandescent point where it iscapable of igniting a fuelair mixture present in combustion chamber 14.The starting motor 12 rotates the compressor of the gas turbine engine11 to supply the air for the combustion chamber 14 and fuel is fed tothe combustion chamber from any suitable source (not shown).

When the gas turbine engine is capable of running under its own power,the starting motor 12 and the glow plug igniter 15 may be deenergized byopening the hand switch 27.

The present invention may employ components having the following valueswhich are given by way of example only. For example, the starting motor12 and the battery 16 may be of such size that the motor will draw from1300 to 1850 amperes when it is energized. The electrical conductor 33may be a low resistance cable having a resistance of approximately 0.001ohm while the glow piling igniter may have a resistance of approximately0.04 o

The following table discloses the starting motor current, the voltagedrop across the conductor 33, and the power dissipated by the glow plug15 during the first twelve seconds of a starting cycle.

Voltage drop Power dissipa- Starting across contion of glow Time,seconds motor ductor 33, lug igniter current, having 0.001 aving 0.04

amps ohm resistance ohm resistance in watts It is apparent from aninspection of the table that the transient current drawn by the motor atthe beginning of the starting cycle provides higher power dissipationand hence enables the igniter to reach higher operating temperaturesfaster than if the igniter were operated at a constant voltage. A goodigniter can operate at steady state over a 2:1 extreme voltage ratio,and as is apparent from an inspection of the table, the peak voltagesupplied to the igniter is less than two times the voltage after nearsteady state conditions have been reached in twelve seconds.

The present invention thus provides a simple and inexpensive startingand ignition system for a gas turbine engine in which an igniter isenergized from a low voltage-high current source simultaneously with theenergization of an electrical power means connected to start the gasturbine engine.

It will be understood that the invention is not to be limited to theexact construction shown and described, but that various changes andmodifications may be made without departing from the spirit and scope ofthe invention as defined in the appended claim.

I claim:

In an ignition system for a gas turbine engine, a starting motor, asource of electrical energy for energizing said starting motor,an'ignition switch having a first terminal connected to said source ofelectrical energy, an electrical conductor connected to a secondterminal of said ignition switch and to a terminal of said startingmotor, said gas turbine engine including a combustion chamber, a glowplug igniter positioned in said combustion chamber and being connectedacross said electrical conductor with one terminal thereof connected tosaid second terminal of said ignition switch and with the other terminalthereof connected to said terminal of the starting motor.

References Cited in the file of this patent UNITED STATES PATENTS2,443,648 Austin et al. June 22, 1948 2,613,499 Lawter Oct. 14, 19522,717,581 Edwards Sept. 13, 1955 2,730,862 Lamy Ian. 17, 1956 2,808,702Dotson Oct. 8, 1957 2,924,935 Moore Feb. 16, 1960 2,928,240 Burton et a1Mar. 15, 1960 2,935,843 Haviland May 10, 1960 2,962,597 Evans -2 Nov.29, 1960

